Self-aligned multipart combustible casting pattern and method of making same

ABSTRACT

Combustible patterns of expanded polystyrene, carved to complex forms by the tape-controlled milling of two or more self-aligning parts, resist displacement from each other as sand is packed within and around them. Tongue-and-groove joints, formed on the mating surfaces of the parts, locate and align the parts and prevent their displacement more surely than adhesives, which tend to cause inclusions and voids in the casting. Adhesive may be coated on the tongue-and-groove parts only, leaving adjacent margins of the mating surfaces free from adhesive; and the exterior surfaces of the assembled pattern may be coated with a noncombustible ceramic coating. The marginal spacing of the adhesive inward from such coating permits quick dispersion of the adhesive when the molten metal is cast.

United States Patent Parsons 51 Jan. 18, 1972 FOREIGN PATENTS ORAPPLICATIONS 1,220,970 7/l 966 Germany 164/34 Primary ExaminerRobert D.Baldwin Att0rneyJerome A. Gross [57] ABSTRACT Combustible patterns ofexpanded polystyrene, carved to complex forms by the tape-controlledmilling of two or more self-aligning parts, resist displacement fromeach other as sand is packed within and around them. Tongue-ancl-groovejoints, formed on the mating surfaces of the parts, locate and align theparts and prevent their displacement more surely than adhesives, whichtend to cause inclusions and voids in the casting. Adhesive may becoated on the tongue-and-groove parts only, leaving adjacent margins ofthe mating surfaces free from adhesive; and the exterior surfaces of theassembled pattern may be coated with a noncombustible ceramic coating.The marginal spacing of the adhesive inward from such coating permitsquick dispersion of the adhesive when the molten metal is cast.

4 Claims, 2 Drawing Figures r I r i I"; I/1i; 52

PATENTED JAN 1 a 1972 J OHM AQ N @%%A 1 SELF-ALIGNED MULTIPARTCOMBUSTIBLE CASTING PATTERN AND METHOD OF MAKING SAME BACKGROUND OF THEINVENTION This invention relates to the making of combustible patternsfor castings, using materials such as expanded polystyrene; andparticularly to the secure alignment of such patterns assembled ofseveral parts. To minimize the problem of alignment, l assemble suchpatterns of preferably only two parts, each carved to a complex shapeaccording to the method dis- .closed in my copending application, Ser.No. 867,980, filed Oct. 20, 1969, entitled Use of Tape ControlledMilling Machines to Carve Combustible Casting Patterns, of which thisapplication is a continuation-in-part.

Some pattern forms, such as hollow boxlike objects having substantialwall portions on six sides, cannot be carved integrally. If patterns aremade to such forms by gluing together boards of low-density polystyrenematerial, in much the same manner as wooden patterns have been made,there is a serious danger that insufficient adhesion will result indisplacement of the pattern parts as the sand is packed within andaround the pattern. Such displacement is not likely to be discovereduntil after the casting has been poured and the pattern burned away.

Expanded polystyrene pattern material is not readily adhered by knownadhesives; and as a further complication, the amount of adhesive must beminimized. Conventional adhesives do not vaporize at the same lowtemperature as the expanded polystyrene material. When the molten metalis cast, the adhesive present must be harmlessly dispersed through it,otherwise voids in the casting may result. Dispersion of the adhesivesis interfered with whenever there is contact between the adhesive and anoncombustible coating material which is conventionally sprayed onto theexterior surfaces of polystyrene patterns.

Heretofore, there has been no satisfactory solution of the problem as tohow to avoid displacement of pattern parts when the sand is packed; andthe use of adhesives has added its own complications to the problem.Such use of adhesive is shown in US. Pat. No. 2,830,343 to Shroyer,which also discloses doweling or wiring the pattern parts together.

SUMMARY OF THE INVENTION A principal purpose of the present invention isto provide self-aligning multipart combustible patterns, which willresist the forces of packing sand into and around them. Further purposesare to provide securely assembled mullipart patterns with a minimum ofadhesive, located spacedly away from noncombustible coatings, so thatthe adhesive will be quickly dispersed within the molten metal and causeno defects in the casting.

l accomplish these purposes by a method in which two or more parts areformed to shapes which when assembled will make up the desired patternform. The parts having mating surfaces carved with interfittingportions, which locate and align the parts with the mating surfaces incontact with each other. The alignment is so positive and strong thatforces encountered in foundry practices, particularly forces attendantto packing sand in and about the pattern, are resisted by theinterfitting parts, without danger of misaligning them. Where adhesiveis to be used, I apply it only to the interfitting tongueand-grooveportions, leaving margins of the mating surfaces without any adhesivecoating; and I form the tongue-andgroove portions to negative tolerancesso that excess adhesive will not penetrate into the margins of themating surfaces. Thereafter when a noncombustible coating is applied tothe exterior surfaces, the adhesive will be so spaced inwardly of thecoating as to avoid adhesion to the coating; when the pattern issubjected to a charge of molten metal, the small quanti ty of adhesivewill be harmlessly dispersed through the metal.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a perspective view, partly broken away, of two pattern parts,carved of combustible pattern material, having the tongue-and-grooveinterfitting alignment means of the present invention.

FIG. 2 is an enlarged fragmentary cross section of an assembled pattern,with molding sand packed thereabout, including adhesive within thetongueand-groove mating parts only.

DESCRIPTION OF THE PREFERRED EMBODIMENT Intricate pattern forms may,according to the present invention, be made up of only two patternparts, each carved from a block of expanded polystyrene material, usinga tape-controlled milling machine in the manner described in mycopending application referred to hereinabove. Two such pattern partsare shown in FIG. I, the lower part being generally designated 10 andthe upper part being generally designated 11. Unlike the somewhatsimilar parts carved as described in said copending application, thelower and upper parts 10, II have integral interfitting provisions,hereinafter described. Each part 10, 11 is formed to an open boxlikeshape with vertical sidewalls and vertical webs in alignment with eachother. Thus, the vertical walls of the lower pattern part 10 have innersurfaces 12 and outer surfaces 13 parallel thereto, carved to be inalignment with the inner surfaces 14 and outer surfaces 15 of the upperpattern part 11. Similarly, vertical webs formed within the lowerpattern part 10 have parallel opposite web wall surfaces 16, 17; and thecorresponding webs in the upper pattern part 12 have opposite wallsurfaces 18, 19 in alignment therewith.

Connecting the upper edges of the wall surfaces 12, 13, I6, 17 of thelower pattern part 10 is a mating surface generally designated 21; acorresponding mating surface 22 connects the lower edges of the wallsl4, 15, 18, 19 of the upper pattern part 11. Midway between the opposedwall surfaces, there is carved on the mating surface 21, an upwardlyprojecting continuous interfit provision. The preferred interfitprovision is a tongue generally designated 23, having beveled sidesurfaces 24 and a horizontal top surface 25. Between the tongue 23 andthe inner and outer wall surfaces 12, 13 horizontal marginal portions 26are provided, to fit tightly against similar marginal portions on theupper pattern part 12, as will be described. These marginal portionsalso provide a spacing between an adhesive coating 28 which may beapplied onto the tongue 23, and a noncombustible coating, hereafterdescribed, to be applied to the wall surfaces 12, 13.

Similarly, the corresponding mating surface 22 of the upper pattern part11 has a continuous groove 31 which receives and mates with the tongue23. The groove 31 has beveled sidewalls 32 and a horizontal top wall 33.Like the tongue 23 on the lower pattern part 10, the groove 31 islocated spacedly between the inner and outer walls 14, 15 of the upperpattern part 11, leaving marginal portions 35. On assembly, these abutsnugly against the marginal portions 26 of the mating surface 21 of thelower pattern part 10, without any adhesive therebetween.

As shown in the enlarged fragmentary view FIG. 2, the tongue 23 andgroove 31 are formed to negative tolerances. The result is that space isprovided for the flow of any excess adhesive. In FIG. 2 such excessadhesive from the coating 28 is shown as accumulated in the space at thetop of the tongue 23.

The width of the abutting marginal portions 26, 35 is such as to preventinflow to the adhesive coating 28 of a noncombustible coating 37 sprayedon the pattern walls after assembly, as hereinafter described. When thelower and upper pattern parts 10, 11 are carved from billets of expandedpolystyrene material consisting essentially of self-adhered expandedbeads, the width of each of the marginal portions 26, 35 is preferablyat least three times that of an expanded bead. Thus, when the beads ofmaterial are cut by the milling cutter, at least two uncut beads willseparate the spray coating 37 from the adhesive 28.

A spray coating of noncombustible material, usually a ceramic in apartially evaporable carrier, is conventionally applied to the exteriorsurfaces of polystyrene combustible patterns. When the casting is made,the noncombustible material in effect lines the molding sand as thecombustible pattern is burned away. Such a coating 37 is applied to thewall surfaces of the pattern parts 11, 12 and covers the junctures ofthe mating surfaces 21, 22.

While expanded polystyrene material is not readily adhered by adhesives,such adhesives cannot be used in large quantities. Their vaporizationtemperatures are higher than that of the polystyrene. If not quicklydispersed throughout the charge of molten metal, they may forminclusions within the castings, resulting in voids.

To disperse the adhesive material harmlessly throughout the moltenmetal, it is important that the adhesive 28 should not adhere to thesprayed on noncombustible coating 37. In the present invention, suchadherence is prevented by the spacing, inwardly of the coating 37, whichis provided by the marginal portions 26, 35. Squeeze-out of the adhesiveinto these margins is avoided by fonning the tongue 23 and groove 31 tonegative tolerances.

Even without use of any adhesive, the pattern parts 10, 11 areself-aligning and resist the lateral forces, such as those applied inpacking sand 36 preparatory to casting. Thus, whether or not any suchadhesive coating 28 is used, the lower and upper pattern parts 10, 11are placed together in a large box, or flask of molding sand; and, withaccess through pattern openings generally designated 38 in the bottomwall 39 of the lower casting part and in the top wall 40 of the uppercasting part 11, sand 36 is packed, by hand, in place against theopposite pattern walls l2, 13, 14, as shown in FIG. 2. Were it not forthe interfitting tongue 23 and groove 31, the lower casting part 10 andupper casting part 11 would be likely to be dislodged out of thealignment, regardless whether adhesive was employed. The interfittingtongue and groove, 23, 31 not only positively locates the lower andupper parts 10, 11 in alignment, but holds them in alignment and resiststhe lateral forces attendant to packing sand within and about them.Thereafter when the casting is poured, if any adhesive has been used onthe tongue 23, it will be quickly and readily dispersed in the charge ofmolten metal. None will be in contact with the noncombustible coating 37and hence none will be retained by the coating.

Using the method of the present invention, there is no limit on thenumber of parts to be fonned and so assembled to make up the desiredpattern form. The use of a tape-controlled milling machine to carve thecomplex pattern parts 11, 12 makes it possible to minimize the number ofsuch parts, while the interfitting tongue 23 and groove 31 areintegrally carved as part of the program of the machine. The result issound castings, formed without glue inclusions, made from patterns whosecomplex shape involves no danger of displacement as the molding sand ispacked.

lclaim:

1. A self-aligned multipart combustible pattern for foundry use,comprising a plurality of pattern parts formed of material of a typewhich is combustible under a charge of molten metal,

said plurality of parts having mating surfaces and being formed toshapes which, when assembled at such mating surfaces, make up a desiredpattern form having shaped exterior surfaces,

at least one of said plurality of parts having opposed wall surfacesterminating in one of said mating surfaces,

tongue-and-groove means formed on the said mating surfaces and spacedinward of the opposed wall surfaces of said one part, whereby to providemarginal mating surface portions therebetween,

an adhesive coating joining the tongue-and-groove means,

the said marginal mating surface portions being free of said adhesivecoating, and a noncombustible coating on said extenor surfaces andcovering the junctures thereat of said marginal mating surface portions,whereby the spacing of the said adhesive coating from the noncombustiblecoating avoids retention of the adhesive when the assembled pattern issubjected to a charge of molten metal. 2. A self-aligned multipartcombustible pattern as defined in claim 1, wherein the tongue-and-groovemeans is formed to negative tolerances, whereby to provide space for theflow of adhesive and thereby maintain the said marginal portions free ofadhesive. 3. A self-aligned multipart combustible pattern as defined inclaim 1, wherein the material from which the pattern parts are formedconsists of self-adhered beads of expanded polystyrene, and in which themarginal portions of the mating surfaces have a width at least threetimes the diameter of such beads. 4. The method of making a multipartself-aligned combustible pattern for foundry use, comprising the stepsof forming from expanded plastic material, of a type which iscombustible under a charge of molten metal, a plurality of pattern partshaving mating surfaces and being so shaped as, when assembled, will makeup the desired pattern form, while so forming the parts, forming ontheir said mating surfaces tongue-and-groove interfitting portionsleaving marginal portions of the mating surfaces thereadjacent, coatingan adhesive on said interfitting portions only, superposing theplurality of parts upon each other whereby the interfitting portionslocate and align the parts in the desired form and the marginal portionsabut each other without any adhesive therebetween, and coating theexterior surfaces of the assembled pattern parts with a noncombustiblecoating, whereby the marginal portions establish a spacing between theadhesive on the interfitting portions and the noncombustible coating.

1. A self-aligned multipart combustible pattern for foundry use,comprising a plurality of pattern parts formed of material of a typewhich is combustible under a charge of molten metal, said plurality ofparts having mating surfaces and being formed to shapes which, whenassembled at such mating surfaces, make up a desired pattern form havingshaped exterior surfaces, at least one of said plurality of parts havingopposed wall surfaces terminating in one of said mating surfaces,tongue-and-groove means formed on the said mating surfaces and spacedinward of the opposed wall surfaces of said one part, whereby to providemarginal mating surface portions therebetween, an adhesive coatingjoining the tongue-and-groove means, the said marginal mating surfaceportions being free of said adhesive coating, and a noncombustiblecoating on said exterior surfaces and covering the junctures thereat ofsaid marginal mating surface portions, whereby the spacing of the saidadhesive coating from the noncombustible coating avoids retention of theadhesive when the assembled pattern is subjected to a charge of moltenmetal.
 2. A self-aligned multipart combustible pattern as defined inclaim 1, wherein the tongue-and-groove means is formed to negativetolerances, whereby to provide space for the flow of adhesive andthereby maintain the said marginal portions free of adhesive.
 3. Aself-aligned multipart combustible pattern as defined in claim 1,wherein the material from which the pattern parts are formed consists ofself-adhered beads of expanded polystyrene, and in which the marginalportions of the mating surfaces have a width at least three times thediameter of such beads.
 4. The method of making a multipart self-alignedcombustible pattern for foundry use, comprising the steps of formingfrom expanded plastic material, of a type which is combustible under acharge of molten metal, a plurality of pattern parts having matingsurfaces and being so shaped as, when assembled, will make up thedesired pattern form, while so forming the parts, forming on their saidmating surfaces tongue-and-groove interfitting portions leaving marginalportions of the mating surfaces thereadjacent, coating an adhesive onsaid interfitting portions only, superposing the plurality of parts uponeach other whereby the interfitting portions locate and align the partsin the desired form and the marginal portions abut each other withoutany adhesive therebetween, and coating the exterior surfaces of theassembled pattern parts with a noncombustible coating, whereby themarginal portions establish a spacing between the adhesive on theinterfitting portions and the noncombustible coating.